1. Field of the Invention
The present invention relates to a method for preventing the corrosion of metal lines, especially relates to a method for preventing metal lines placed at the edge of a color filter on the substrate of liquid crystal display from corroding.
2. Description of the Related Art
Liquid crystal display (hereinafter referred to as LCD) is a widely-used flat display technology. Since LCD units are light and thin with the advantages of low power consumption and low driving voltage, they are enormously popular in a variety of applications such as notebooks, digital cameras, video games, projectors, and numerous other applications. There are, however, some problems related to the fabrication of LCDs. One is that metal lines placed at the edge of the color filter (hereinafter referred to as the CF) on the LCD substrate are often corroded. FIG. 1 is a top view illustrating the corrosion 12d of metal lines 12a, 12b and 12c placed close to the edge of the CF 13 on a conventional LCD substrate. The corrosion occurring on the metal lines is caused by various conditions. First, since cracks are formed in the passivation layer by the stress generated during the CF edge cutting process, vapor and other corrosive materials may permeate through the cracks and corrode the metal lines. Second, since micro-contamination is not completely eliminated during the LCD manufacturing process. micro-contamination remaining in the deposited layers will cause cracks. FIG. 2 is a cross-sectional diagram of the metal line 12a placed at the edge of the CF on a conventional LCD substrate. In the manufacturing process of a conventional LCD, the metal line placed at the edge of the CF on the LCD substrate normally constitutes a structure as shown in FIG. 2. That is, the metal line 12a is formed on the substrate 10, and then an insulating layer 14 and a passivation layer 16 are sequentially formed on the metal line 12a. Referring to FIG. 2, once the cracks 18 are formed in the passivation layer 16, vapor, air or other corrosive material will permeate through the passivation layer 16 and the insulating layer 14 to the metal line 12a and electrolyze the metal line, causing the occurrence of corrosion on the metal line. The metal line is apt to be broken or badly connected once being corroded, thus significantly degrading the reliability of the LCD.
Prior-art methods used to overcome the above problem can be classified as follows.
First, in order to prevent metal line corrosion, macrocontamination is completely eliminated by strict control of the manufacturing process.
Second, a waterproof agent is introduced at the edge of the CF to protect the metal line from macro-contamination and vapor.
Production costs, however, increase when the manufacturing process is strictly controlled as in the first prior-art method. Similarly, production costs also increase in the second prior-art method with the addition of the step involving the introduction of the waterproof agent. Therefore, improving the reliability of LCD units without increasing the production costs or changing the conditions of the manufacturing process is a critical issue relating to the fabrication of LCDS.
Accordingly, an object of the present invention is to provide a method for protecting metal lines from corrosion without increasing production costs or changing the conditions of the manufacturing process of LCDs.
In order to achieve the above object, at least one passivation layer and at least one semiconductor layer are formed on a predetermined area at the edge of the CF to prevent vapor or other corrosive materials from permeating the metal lines. Therefore, the metal lines will not be broken or suffer conductivity degradation, since no corrosion occurs, thus significantly increasing the reliability of LCDs.